The present invention relates to an image exposing apparatus which focuses and exposes an image onto a photosensitive member through a converging optical system having a plurality of focusing light transmission media arranged in a line.
A converging light transmission medium known by the tradename Selfocs of Nippon Sheet Glass is an elongated cylindrical optical element whose coefficient of refraction parabolically changes in radial direction around a center axis. It is cut to an appropriate length to impart a focusing function. An array having a number of such light transmission media is applied to an electrophotographic copying machine or a document reader using an image sensor, as an optical system for exposing a document image.
In FIG. 1, light transmission media 1 described above are arranged in a line and molded in a support 2 of resin. The light intensity distribution of an image on a photosensitive member effected by such an array is the sum of the light intensity distributions of images formed by individual light transmission media, as shown by a curve E in FIG. 2. As shown, the light intensity distribution is highest at an area corresponding to the center of each light transmission medium and lowest at an area corresponding to the boundary of adjacent light transmission media. The distribution is rippled and the distribution period thereof corresponds to an arrangement period of the light transmission media. Because of the rippled light intensity distribution, an formed image includes a periodic stripe pattern. In the past, two layers of such light transmission media are stacked in a zig-zag fashion. This requires double expensive light transmission media and increases its size.